Manganese-activated, red-emitting fluoride phosphors have recently emerged as an important class of LED down-converters due to their narrow-band spectral emission, high photoluminescence efficiency, and low thermal quenching. When incorporated into LED components, these phosphors can enhance the performance of both lighting and display products. Of this class of materials, manganese-activated potassium fluorosilicate (KSF:Mn) is the most notable, having become commercially available in the past few years.
For lighting applications, KSF:Mn enables warm-white LED components with high luminous efficacy (lm/W) while preserving a high color rendering index (CRI), typically greater than 90. The phosphor's narrow red emission band results in less “wasted” light emitted into the far-red and infrared when compared to conventional phosphors. In displays, KSF:Mn enables a wider color gamut due to its saturated narrow band emission.
Yet the wide-spread commercial adoption of KSF:Mn in solid state lighting has been limited, in part, by the reliability of the material, which is sensitive to moisture, high temperature, and high blue-flux density. When exposed to water, for example, the manganese activator can rapidly discolor, resulting in a dramatic decline in performance. Furthermore, the fluorosilicate host can generate corrosive fluoride species which pose a threat to the various sensitive materials found in LED components.